The genomic consequences of adaptive divergence and reproductive isolation between species of manakins.

The processes of adaptation and speciation are expected to shape genomic variation within and between diverging species. Here we analyze genomic heterogeneity of genetic differentiation and introgression in a hybrid zone between two bird species (Manacus candei and M. vitellinus) using 59 100 SNPs, a whole genome assembly, and Bayesian models. Measures of genetic differentiation (FST) and introgression (genomic cline center [α] and rate [ß]) were highly heterogeneous among loci. We identified thousands of loci with elevated parameter estimates, some of which are likely to be associated with variation in fitness in Manacus populations. To analyze the genomic organization of differentiation and introgression, we mapped SNPs onto a draft assembly of the M. vitellinus genome. Estimates of FST, α, and ß were autocorrelated at very short physical distances (< 100 bp), but much less so beyond this. In addition, average statistical associations (linkage disequilibrium) between SNPs were generally low and were not higher in admixed populations than in populations of the parental species. Although they did not occur with a constant probability across the genome, loci with elevated FST, α, and ß were not strongly co-localized in the genome. Contrary to verbal models that predict clustering of loci involved in adaptation and isolation in discrete genomic regions, these results are consistent with the hypothesis that genetic regions involved in adaptive divergence and reproductive isolation are scattered throughout the genome. We also found that many loci were characterized by both exceptional genetic differentiation and introgression, consistent with the hypothesis that loci involved in isolation are also often characterized by a history of divergent selection. However, the concordance between isolation and differentiation was only partial, indicating a complex architecture and history of loci involved in isolation.

Interaction between female mating preferences and predation may explain the maintenance of rare males in the pentamorphic fish Poecilia parae.

Variation in mating preferences coupled with selective predation may allow for the maintenance of alternative mating strategies. Males of the South American live-bearing fish Poecilia parae fall in one of five discrete morphs: red, yellow, blue, stripe-coloured tail (parae) and female mimic (immaculata). Field surveys indicate that the red and yellow morphs are the rarest and that their rarity is consistent across years. We explored the role of variable female mating preference and selective predation by visual predators in explaining the rarity of red and yellow males, and more generally, the maintenance of this extreme colour polymorphism. We presented wild-caught P. parae females and Aequidens tetramerus, the most common cichlid predator, with the five male colour morphs in separate trials to determine mating and prey preferences, respectively. We found that a large proportion of females shared a strong preference for the rare carotenoid-based red and yellow males, but a distinct group also preferred the blue and parae morphs. The cichlid predator strongly preferred red and yellow males as prey. Together, these results suggest that the interaction between premating sexual selection favouring and predation acting against the red and yellow morphs may explain their rarity in the wild. The trade-off between sexual and natural selection, accompanied by variation in female mating preferences, may therefore facilitate the maintenance of the striking colour polymorphism in P. parae.

Variable visual habitats may influence the spread of colourful plumage across an avian hybrid zone.

Several studies have shown that hybridization can be a creative process by acting as a conduit for the spread of adaptive traits between species, but few provide the mechanism that favours this spread. In the hybrid zone between the golden- (Manacus vitellinus) and white-collared (Manacus candei) manakins, sexual selection drives the introgression of golden/yellow plumage into the white species; however, the mechanism for the yellow male's mating advantage and the reasons why yellow plumage has not swept further into the white species remain mostly speculative. We quantified the colour properties of male plumage, the background and the ambient light at the hybrid zone, and allopatric golden and white populations. As measured by the perceived difference in colour between plumage and background, we found that yellow plumage appears more conspicuous than white plumage in the hybrid zone and allopatric golden-collar habitats, whereas white plumage appears more conspicuous than yellow plumage in the allopatric white-collared habitat. These results suggest a mechanism for the unidirectional spread of yellow plumage across the hybrid zone but slowed movement beyond it.

Loss of preferred mates forces female satin bowerbirds (Ptilonorhynchus violaceus) to increase mate searching.

Variation in mate choice among females can have important consequences for the operation of sexual selection, and can result from differences in the way females search for mates. Our previous work indicates that female satin bowerbirds Ptilonorhynchus violaceus alter their mate-searching patterns according to long-term experience. Females which mate with very attractive males mate with the same males in the following year, thereby reducing their search. In contrast, females which fail to encounter very attractive males typically reject their previous mates and search for more attractive males in the following year, thereby increasing their search. Here we report results from a natural experiment consistent with these observations. Five males, including the most attractive male of 1997, failed to re-establish display sites in 1998, most probably dying over winter. We monitored the mate-searching behaviour of females which mated with these males in 1997 to determine how the loss of attractive mates affects subsequent mate-searching patterns. Females which lost their mates sampled more males compared with their own search patterns in 1997 and with faithful females in 1998. Results from this natural experiment indicate that the loss of attractive and preferred mates forces females to increase their search and provide evidence that long-term experience with males shapes mate-searching behaviour.

Complex mate searching in the satin bowerbird Ptilonorhynchus violaceus.

Mate-choice studies typically focus on male traits affecting female mating decisions, but few studies seek to identify the behavioral rules females use when searching for mates. Current models suggest that females may either directly compare a set of males ("pooled comparison") or compare each male to an internal standard ("sequential-search rule") when judging the suitability of potential mates. Models also differ in other specific aspects, such as the predicted number of sampling bouts initiated and the tendency of females to return to males after previous visits. We monitored 63 female satin bowerbirds, Ptilonorhynchus violaceus, during mate sampling to reconstruct their search patterns. We found that females typically sampled several males and returned to the most attractive male for mating: a behavior consistent with the pooled-comparison tactic. Females, however, varied in the number of males sampled; some visited only one male before mating. We found that this variation can be explained by differences among females in the number of mates, the date mate searching is initiated, and long-term experience with males. Further, females were observed to initiate two distinct sampling bouts, with the rejection of most of their potential mates occurring before the start of the second sampling bout. This suggests that the choices of potential mates are narrowed prior to the second sampling bout and that the later visits may function to reconsider preliminary decisions made during the first sampling bout or to resolve decisions concerning the remaining potential mates. Our results indicate that mate searching is a complex process in which females use multiple sampling bouts to find suitable mates and in which several different factors influence their search behavior.

Sexual selection drives rapid divergence in bowerbird display traits.

Sexual selection driving display trait divergence has been suggested as a cause of rapid speciation, but there is limited supporting evidence for this from natural populations. Where speciation by sexual selection has occurred in newly diverged populations, we expect that there will be significant differences in female preferences and corresponding male display traits in the absence of substantial genetic and other morphological differentiation. Two allopatric populations of the Vogelkop bowerbird, Amblyornis inornatus, show large, qualitative differences in a suite of display traits including bower structure and decorations. We experimentally demonstrate distinct male decoration color preferences within each population, provide direct evidence of female preferences for divergent decoration and bower traits in the population with more elaborate display, and show that there is minimal genetic differentiation between these populations. These results support the speciation by sexual selection hypothesis and are most consistent with the hypothesis that changes in male display have been driven by divergent female choice.

Dynamic mate-searching tactic allows female satin bowerbirds Ptilonorhynchus violaceus to reduce searching.

Females can maximize the benefits of mate choice by finding high-quality mates while using search tactics that limit the costs of searching for mates. Mate-searching models indicate that specific search tactics would best optimize this trade-off under different conditions. These models do not, however, consider that females may use information from previous years to improve mate searching and reduce search costs in subsequent years. We followed female satin bowerbirds Ptilonorhynchus violaceus during mate searching and reconstructed their search patterns. We found that females who chose very attractive males typically mated with the same male in the following year, resulting in these females sampling fewer males than those who switched mates. In contrast, females who mated with less attractive males typically rejected their previous mates and searched longer for more attractive mates in the following mating season. A potential cost to mate searching is suggested by the observed increase in the likelihood of force-copulation attempts from marauding males with increased searching. Our results suggest that by using past experiences to adjust their search tactics, females may obtain high-quality mates while limiting search costs. These results emphasize the need to consider historical effects in studies of sexual selection, especially for long-lived species with stable display sites.